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Date: Wed, 13 Nov 2002
Posted by: Barbara Ray (brayowc@earthlink.net)

Regarding point #7 of Mr.Robbins' message is that using dead crows as a surveillance tool is only useful in areas where crows are the most affected species. Out west, for example, the primary vector for WNV is likely to be C. tarsalis, a species which feeds primarily on mammals. So it is not inconceivable that the corvids could be largely unaffected compared to the eastern half of the country.

As far as the efficacy of larvacide and adulticide mosquito control, in Ohio we have seen Lake County initiate mosquito abatement as soon as WNV was reported in the state and they experienced about 7 positive human cases. Cuyahoga county, right next door, uses no abatement program and experienced over 300 positive human cases. Cuyahoga also has a larger human population, so perhaps these numbers are not as valuable as they sound, and certainly many cases go unreported as well as the fact that under random (sera) testing (if it were done), many cases would test positive that are not indicative of infection but merely exposure. In other words, we always have more questions than answers!

In Central Ohio, we are making a concerted effort to encourage communities to initiate abatement programs beginning early next spring using bacterial larvacides and the species-specific trypsin modulating oostatic factor compounds being developed that interferes with the female reproductive cycle in mosquitoes, as well as eliminating potential breeding sites. As the drought here finally proved to many non-believers in this area, some species thrive during dry conditions because what breeding sites there are are heavily concentrated with the organisms the larva need and they tend to survive in tenfold numbers as they also have little preying on them.

Barbara Ray
Ohio Wildlife Center

Norman Robbins wrote:

Dear West Nile List-Servers,

As a scientist, I am greatly disturbed to read lengthy discussions and CDC or State recommendations for WNv actions that often appear to be based mainly on opinion rather than citations of statistical validation. As much as one prefers prospective studies, could a thorough and sophisticated CDC retrospective analysis of activities (e.g. larviciding, adulticiding in 1999-2002) and resulting mosquito density and human disease, shed some light on questions we will once again be debating in the next few months?

I encourage List-servers to revise or expand the following list of questions in the hope that a collated version can be signed by you and sent to CDC advocating that they use resources to investigate these issues. My sense is that the CDC people are not at all resistant to undertaking this analysis -- they just need outside advocacy to gain the resources.

QUESTIONS FOR CDC TO INVESTIGATE BY ANALYSIS OF WEST NILE DATA TO DATE:

What is the STATISTICAL EVIDENCE AND PROBABILITY RANGE (not opinion) that:

1. larviciding (at WHAT intensity and frequency) reduces mosquito populations (by species)?

2. URBAN adulticiding (at what intensity, frequency, area and method) reduces mosquito populations, by species and for how long?

3. there are (or are not) acute or chronic human health effects of urban adulticiding in typical ULV amounts and frequency?

4. certain types of public messages or policies are more or less effective than others in reducing urban standing water (residential, public spaces, etc.)

5. one or another type of surveillance (dead crows, gravid or C0-2/light traps, virus-positive mosquitoes, etc.) predicts human disease with what kind of probability range.

6. both gravid and C0₂/light traps are desirable for human disease prediction.

7. there is some level of mosquito density which predicts risk of animal or human disease and calls for more aggressive mosquito management

Norman Robbins
Shaker Heights (OH) West Nile Task Force

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